1. Field of the Invention
The present invention concerns a hearing aid device of the type having a voltage supply that can be used to supply an external device that can be connected to the hearing aid device. The present invention also concerns a method for operation of such as external device connected to the hearing aid device.
2. Description of the Prior Art
Hearing aid device that are worn behind the ear in many cases have in the most cases an audio input that serves for the connection of external signal sources thereto. External signal sources are, for example, CROS (contraradial routing of signals) microphones, audio devices, FM transmission systems, etc. Some of these connected devices require a supply voltage delivered from the hearing aid device. Of these, for example, the CROS microphones require an extremely stable supply voltage with a relatively low current consumption. Thus a current requirement of up to approximately 300 μA exists for three microphones. Such a regulated voltage supply in this current range can be ensured using typical voltage regulators.
Other external devices that can be connected to the hearing aid device, such as, for example, miniature FM receivers, require a significantly higher current consumption of, for example, 1 to 2 mA. Since a voltage regulator exhibits a high-ohmic source impedance, such that the voltage would drop significantly given such high currents, a conventional voltage regulator is not suitable as a voltage source for these devices. For this reason, the unregulated battery voltage is provided for such devices at the audio input of the hearing aid device.
Heretofore, hearing aid devices typically have been equipped with a regulated supply voltage at the audio input, since predominantly CROS microphones with lower current consumption were the devices to be supplied therefrom. As small miniature FM systems later came onto the market, the hearing aid devices had to be correspondingly retrofitted for use with these systems. Modern hearing aid devices therefore are already provided with an unregulated supply voltage at the audio input. If the need arises to supply a CROS microphone, special microphone devices with internal voltage stabilization are therefore necessary.
From German OS 37 05 478, an electronic hearing apparatus with four connections is known, of which a first connection is connected with a first signal source that is, for example, a radio apparatus, a recorder, a radio or a warning device. A second connection is connected with a microphone and the third is connected with a computer. The fourth connection and, if applicable, further connections are provided for the connection of further signal sources.
From German Translation 690 31 227, a hearing aid is known with a switching circuit to which external components such as an on-off switch and a contact point are connected. The contact point is connected via a switching circuit connection with a voltage source that supplies the circuits in the switching circuit with various regulated voltages.
From German OS 102 11 364, an apparatus is known for deactivation of signal-processing devices of a hearing device. This device has a monitoring logic for activation and deactivation of a hearing device signal source.
Some hearing aid devices provide both a regulated and an unregulated supply voltage at the audio input. A disadvantage in such devices is that an additional audio contact is necessary, such that the audio input typically exhibits the following four contacts: signal contact, ground contact and two voltage supply contacts. A further disadvantage when both supply voltages must be provided is that a separate audio shoe or adapter, which serves to provide either the regulated or the unregulated operating voltage for the connected device, must be provided for each application case.